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This is the executive summary from a technical report produced for the Puget Sound Nearshore Partnership on Valued Ecosystem Components (VEC). The entire document is included as a PDF with this summary.

Dungeness crabs are an important resource in Puget Sound for recreational, commercial, and tribal fisheries. They utilize a variety of habitats over the course of their lives, and are vulnerable to shifts in ocean temperature and water quality.

Biology/Natural History: This crab is the largest edible crab from Alaska to California, making this species important for fisheries commercially and economically. There appears to be five subspecies in California alone. The female Dungeness crab can lay up to 2.5 million eggs and can live up to at least 6 years. Females can store sperm received during one mating season and use it during the next season. This species is a carnivore that feeds on more than 40 different species including small clams, oysters, fish, shrimp, worms and according to recent studies even feeds on Velella nematocysts. The larvae of this species is often attached to the bells of jelly fishes and to their tentacles; these larvae feed on the gonozooids, and by doing so gain protection from pelagic fish predators and are transported to juvenile crab habitats nearshore as long as associated with the cnidarian. Dungeness crab larvae feed primarily on zooplankton, however phytoplankton are also eaten. The larvae are crepuscular migrators, being found near the surface at dawn and dusk but deeper in midday and midnight. The stage 1 zoeae are nearest the surface with later zoeal stages in deeper water. In spring, larvae of this species may be advected north along the coast as far as Alaska (Park et al., 2007). In springtime, adults of this crab can be found buried in sand or in tidepools, where it can hide and wait for its new shell to harden. On average, males will cover more ground in an hour than females, and ovigerous females move less than nonovigerous females or males. Near Vancouver Island, adults have more epibionts than do juveniles (McGraw, 2006). Common epibionts include barnacles (especially Balanus crenatus) on the dorsal surface, green, red, and brown algae (especially on the antennae), tube-dwelling polychaetes (mainly on the ventral surfaces), hydrozoans (mainly on ventral surfaces and limbs), bryozoans (especially Membranipora membranacea) on any region of the carapace. A few had sponge, tunicate, or mollusk epibionts.

A Red-brown to purple carapace with a spine-tipped edge on the front half; contains ten small teeth on the anterolateral margins; tenth tooth is the most prominent. There are no teeth on the posterolateral margins. Width of carapace up to 23 cm. Chelipeds are purple to brownish at the base and the hands are white with purple. The carpus, propodus, and dactyl of the chelae have spiny ridges. This species alone accounts for more than 99 percent of all crab species taken for commercial reasons.

References:

Wicksten,Mary K., 2009. ; Decapod Crustacea of the Californian and OregonianZoogeographic Provinces. ; UC San Diego Scripps Institution of OceanographyLibrary, Scripps Institution of Oceanography. ; http://escholarship.org/uc/item/7sk92dz ;418 pages. ; Published online only. ; This excellent key coversdecapods (crustaceans such as crabs, shrimp, spiny lobsters, hermit crabs,and crayfish) from shallow and deep water from Puget Sound south to thePacific coast of Baja California. ; Includes many subkeys, drawings,and photos. ; No glossary, table of contents, or index. ; Thisis the place to go for the most up-to-date key for decapods. ; MaryWicksten plans to publish an updated version of this key soon.

Hart, Josephine F.L., 1982. ;Crabs and their relatives of British Columbia. ; British Columbia ProvincialMuseum Handbook 40. ; Paperback. ; 267 pages. ; This smallpaperback contains keys and individual descriptions and drawings of 95species of true crabs, hermit crabs, other anomurans, mud and ghost shrimp(but not shrimp or prawns) found off British Columbia. ; An introductiongives an extensive discussion of the general biology and anatomy of crabsand other similar crustaceans, including topics such as sexual dimorphism,larvae, and parasites. ; A variety of drawings and tables are included. ;The general characteristics of each of the families included in the bookare discussed. ; Keys to the families of each section (Thalassinidea,Anomura, Brachyrua) are included but one needs to know beforehand whichsection the animal is in. ; Keys are also included for the membersof each family. ; A useful key for the serious student wanting to identifycrabs.

Cancer magister, commonly known as Dungeness crab, is found in the costal waters from Point Concepcion, California, to the Pribilof Islands, Alaska. The Dungeness crabs inhabit the estuaries from Morro Bay, California, to Puget Sound, Washington.

Cancer magister is a decapod. Decopods' thoracic segment is fused with that of the head, to form the cephalothorax, which is covered by a carapace. The Dungeness crab has five pairs of thoracic legs. The first pair of legs is larger then the last four and has pinching claws. Cancer magister is a walking crab and therefore, the last pair of legs is adapted for walking. It has a flat and broad body, oval in shape. The anterior margin of the carapace has nine small teeth on each side, forming an elliptical curve. At the end of the curve, a large, pointed tooth projects directly outward. From this tooth, the carapace slopes backward, forming a narrow posterior end. Males range from 18 to 23 centimeters (about 7 to 9 inches)in width and 10 to 13 centimeters (4 to 5 inches) long. The color of the carapace is reddish-brown, fading towards the back. The legs and ventral side are yellowish.

How to Distinguish from Similar Species: A similar, somewhat larger crab is the Furrowed Rock Crab (Romaleon branneri). This species is not common in the intertidal region, unlike M. magister, and differs in that the dactyls of its chelae have black tips and spines that line the upper margin of the movable finger of the claws. Cancer productus, often found in the intertidal in the Pacific Northwest, also has black tips to the dactyls of the chelae. Metacarcinus gracilis has a distinct tooth behind the widest point of the carapace and has no spiny ridges on the carpus, propodus, and dactyl of the chelae.

Dungeness crabs are found on the Pacific coast in sandy bottoms below the tidal mark. They can also be found at lowtide in sandy or muddy bays where there is a good growth of eel grass. Dungeness crabs are intolerant of low dissolved oxygen conditions. Also, even low amounts of ammonia are toxic to the crabs. Dungeness crabs also tend to grow better in water that is above six degrees Celsius (Kozloff 1973).

Cancer magister eat a variety of marine invertebrates and fish. As juveniles, the Dungeness crabs feed on fish, shrimp, molluscs and crustaceans. Adults feed on bivalves, crustaceans and fishes. The crabs are able to open shells by chipping away at them with their heavy pinching claws.

Reproduction

Males attract the females by use of pheromones, which are chemical scents. During mating, the male crabs clasp the female so that the undersides of each are close. The male's breeding structures place the sperm into the female's body. This is only possible when the female is soft shelled, right after molting. This lasts less than thirty minutes. Mating occurs in near-shore costal locations, outside of estuaries. The eggs are not fertilized and spawned until the fall, following the summer breeding. After fertilization, about half a million to one million eggs are attatched to the female's abdomen. These eggs are brooded there until spring. The larvae are planktonic and use tidal currents to travel into estuaries. The larvae pass through six stages over a 105 to 125 day period. The last two stages are zoea and megalopa. Zoea have a jointed abdomen and a spined carapace behind the head with large eyes. Megalops have big eyes, an extended abdomen, elongated carapace and swimming legs. After the first molting, the form changes to that similar to the adults. Growth after this point occurs by shedding its shell, molting, at certain periods of time, until it reahces full growth (Headstrom 1979, Mash 1975).

Dungeness crabs are affected by many insecticides. The insecticide carbaryl, also known as Sevin, is particularly toxic to the Dungeness crab. Other toxins include other insecticides and fungicides as well as ammonia. Urban pollutants such as heavy metals, PCB's and hydrocarbons also affect the Dungeness crab. Runoff of pesticides and herbicides affect the Dungeness crab populations as well. Dungeness crabs are not endangered, however, these chemicals can kill or upset the health of Dungeness crab populations.

NatureServe Conservation Status

Dungeness carbs are an important commercial shellfish. Male crabs are harvested along the coast of North America from Alaska to California. The fishery is worth tens of millions of dollars, due to the thousands of crabs caught annually.